In this study we have evaluated the in vivo ability of triflusal (2-acetoxy-4-tri-fluoromethylbenzoic acid) to inhibit constitutive nuclear factor-kappa B (NF-kappaB) activation in the brain of postnatal rats. One week old Long-Evans black hooded rat pups received three oral administrations of triflusal (30 mg/kg) and were sacrificed at 9 days of age. After fixation, brains were cut in a cryostat and processed immunocytochemically for the demonstration of NF-kappaB. In control postnatal rats, NF-kappaB is constitutively present in some neuronal populations and in glial cells of white matter tracts. In contrast, triflusal treated rats showed a drastic downregulation of neuronal and glial NF-kappaB, both in the number of labelled cells and in the intensity of staining. The inhibition of NF-kappaB activation could be an important step in the modulation of inflammatory processes occurring after several pathological conditions.